FIELD OF THE INVENTION
The invention relates to a method for determining an air mass flow into cylinders of an internal combustion engine with the aid of a model, including an intake system having an intake tube with a throttle valve disposed therein and a throttle position sensor detecting an opening angle of the throttle valve; a sensor generating a load signal of the internal combustion engine; and an electric control device calculating a basic injection time on the basis of a measured load signal and a speed of the internal combustion engine.
Engine management systems for internal combustion engines which operate with fuel injection require the air mass m.sub.Zyl, taken in by the engine as a measure of engine load. That variable forms the basis for realizing a required air/fuel ratio. Increasing demands being placed on engine management systems, such as the reduction in pollutant emission by motor vehicles, lead to the need to determine the load variable for steady-state and non-steady state operations with low permissible errors. In addition to such operation, the exact detection of load during a warming-up phase of the internal combustion engine offers considerable potential for pollutant reduction.
In engine management systems controlled by air mass, in non-steady state operation, the signal of the air mass meter disposed upstream of the intake tube, which is a signal that serves as a load signal of the internal combustion engine, is not a measure of the actual filling of the cylinders, because the volume of the intake tube downstream of the throttle valve acts as an air reservoir which has to be filled and emptied. However, the decisive air mass for calculating the injection time is that air mass which flows out of the intake tube and into the respective cylinder.
Although the output signal of the pressure sensor reproduces the actual pressure conditions in the intake tube in engine management systems controlled by intake tube pressure, the measured variables are not available until relatively late, inter alia because of the required averaging of the measured variable.
The introduction of variable intake systems and variable valve timing mechanisms, for empirically obtained models for acquiring the load variable from measuring signals, has produced a very large multiplicity of influencing variables which influence the corresponding model parameters.
Model-aided computational methods based on physical approaches represent a good starting point for the exact determination of the air mass m.sub.Zyl.
German Published, Non-Prosecuted Patent Application DE 39 19 448 A1, corresponding to U.S. Pat. Nos. 5,003,950 and 5,069,184, discloses a device for the control and advance determination of the quantity of intake air of an internal combustion engine controlled by intake tube pressure, in which the throttle opening angle and the engine speed are used as the basis for calculating the current value of the air taken into the combustion chamber of the engine. That calculated, current quantity of intake air is then used as the basis for calculating the predetermined value of the quantity of intake air which is to be taken into the combustion chamber of the engine at a specific time starting from the point at which the calculation was carried out. The pressure signal, which is measured downstream of the throttle valve, is corrected with the aid of theoretical relationships so that an improvement in the determination of the air mass taken in is achieved and a more accurate calculation of the injection time is thereby possible. However, in non-steady state operation of the internal combustion engine it is desirable to carry out the determination of the air mass flowing into the cylinders even more accurately.